MUSCLE AND NERVOUS TISSUES 163 



other nervous structures. Cerehrin is a term which probably includes 

 several substances, which are nitrogenous glucosides ; they yield on hydrolysis 

 the sugar called galactose (see p. 12). They are sometimes called 

 cerebrosides. The crystalline monatomic alcohol cJwlesterin (see p. 73) is 

 also a fairly abundant constituent of nervous structures, especially of the 

 white substance of Schwann. Finally there are smaller quantities of other 

 extractives, and a small proportion of mineral salts (about 1 per cent, of the 

 solids). 



Fresh nervous tissues are alkaline, but, like most other living structmres, 

 they turn acid after death. The change is particularly rapid in grey matter. 

 The acidity is due to lactic acid. 



Little or nothing is known of the chemical changes nervous tissues 

 tmdergo during activity. We know that oxygen is very essential, especially 

 for the activity of grey matter ; cerebral anaemia is rapidly followed by loss 

 of consciousness and death. "Waller has suggest^ that small quantities of 

 carbonic acid are produced during acti^■ity, because the increase in the action 

 current (detected by the galvanometer) which occurs after a nerve has been 

 repeatedly excited is very like the increase also noted on the application of small 

 quantities of this gas. Waller's statement that the action current is increased 

 by small amounts of carbonic acid has, however, received other explanations. 

 Certainly large quantities of carbonic acid act like an anaesthetic, abolishing 

 nervous activity. Of all parts of the nervous system, the cells in the grey 

 matter are those which most readily manifest fatigue ; the next most sensitive 

 region is the termination of nerves in such endings as the end plates. Fatigue 

 in a medullated nei-ve trunk has never yet been experimentally demonstrated ; 

 Waller's \-iew that this is due to inter-nutritional changes between the axis 

 cylinder and the investing medullary sheath can hardly be considered proved, 

 for it is just as diflScult to demonstrate fatigue in non-medullated nerves. 



Chemistry of nerve-degeneratioii. — Mott and I have shown that in the 

 disease General Paralysis of the Insane, the marked degeneration that occurs 

 in the brain is accompanied by the passing of the products of degeneration 

 into the cerebro-spinal fluid. Of these, nucleo-proteid and choline — a decom- 

 position product of the lecithin (see p. 18) — are those which can be most readily 

 detected. Choline can also be found in the blood. But this is not peculiar 

 to the disease just mentioned, for in various other degenerative nervous 

 diseases (combined sclerosis, disseminated" sclerosis, meningitis, alcoholic 

 neuritis, beri-beri) choline can also be detected in these situations. The 

 tests employed to detect choline are mainly two : (1) a chemical test, namely 

 the obtaining of the characteristic octahedral crystals of the platinum double 

 salt from the alcoholic extract of the cerebro-spinal fluid or blood ; ^ (2) a 



' This test is performed as follows : the fluid is dilated with about five times 

 its volume of alcohol and the precipitated proteids are filtered off. The filtrate is 

 evaporated to dryness at 40° C. and the residue dissolved in absolute alcohol and 

 filtered ; the filtrate from this is again evaporated to dryness, and again dissolved 

 in absolute alcohol, and this should be again repeated. To the final alcoholic solu- 

 tion, an aleohohc solution of platinum chloride is added, and the precipitate so 

 formed is allowed to settle and washed with absolute alcohol by decantation ; the 

 precipitate is then dissolved in 15-per-cent. alcohol, filtered, and the filtrate is 

 allowed to slowly evaporate in a watch-glass at 40° C. The crystals can then be 

 seen with the microscope. They are recognised not only by their vellow colour 



m2 



